1. Technical Field
The present invention relates to a valve system for an internal combustion engine having nonrotatable rocker shafts for mounting rocker arms or finger followers which actuate intake and exhaust popper valves.
2. Description of Prior Art
In designing a valve system or valve train mechanism for an internal combustion engine which is expected to operated at high engine speed, it is necessary to limit component deflections at the maximum rated speed. As an approximation, limiting values could comprise 0.0015 inches deflection for a rocker arm, measured at the valve tip, and 0.00075 inches of deflection of the rocker shaft, measured at the location of the rocker arm. In engines using cylindrical rocker shafts, a typical way of mounting the shafts involves placing the shaft as a slip-fit in a round mounting bore formed in the cylinder head. This causes problems because tolerances permit movement of the rocker shaft of the magnitude recited above. This is undesirable because, as noted above, any loss of stiffness due to wobble or movement of the parts of the valve system will reduce the maximum satisfactory operating speed of the valve system. The present invention mitigates this problem because it provides support for a rocker shaft at three circumferential locations which are approximately equally spaced. The rocker shaft is supported with a robustness which is essentially independent of dimensional tolerances of the rocker shaft and the mounting saddles. In conventional saddle mounting systems in which a nonrotatable rocker shaft is placed in a semicircular saddle, the diameter of the saddle must be sufficient so that the shaft neither touches solely at the bottom of the saddle, in which case the shaft would be free to rock back and forth in the presence of side loading imposed by the rocker arms and valve springs. Also, the shaft should not be pinched between the upper edges of the saddle because this will produce unwanted stresses in both the saddle and the shaft. As a result, it is exceedingly difficult to produce a semicircular saddle and shaft having appropriately sized diameters during mass production of engines. This manufacturing problem, which is present in other systems, is solved by the present invention.